You'd use a greenscreen and AFTER EFFECTS . Check out videocopilot.net for some AE tutorials, I don't think they have a levitation one, but there are other tutes you could tailor to suit your uses.
Greenscreen work on weak codecs is a very bad idea. You'll want to transcode to AT LEAST a 422 colorspace (eg Prores 422 or Cineform on a PC), preferably higher.
Your only other option would be a secure harness attached to a crane of some kind with your attachment method removed in post. This would be more expensive, but look better than the green screen method. But since you're on a lo/no budget, I'd recommend NOT attempting this since you can easily be sued if something were to go wrong and you didn't purchase liability insurance.